Introduction

If type 2 diabetes was an infectious disease, passed from one person to another, public health officials would say we’re in the midst of an epidemic. This difficult disease, once called adult-onset diabetes, is striking an ever-growing number of adults. Even more alarming, it’s now beginning to show up in teenagers and children.

More than 24 million Americans have diabetes; of those, about 6 million don’t know they have the disease. (1) In 2007, diabetes cost the U.S. an estimated $116 billion in excess medical spending, and an additional $58 billion in reduced productivity. (1) If the spread of type 2 diabetes continues at its present rate, the number of people diagnosed with diabetes in the United States will increase from about 16 million in 2005 to 48 million in 2050. (2) Worldwide, the number of adults with diabetes will rise from 285 million in 2010 to 439 million in the year 2030. (3)

The problems behind the numbers are even more alarming. Diabetes is the leading cause of blindness and kidney failure among adults. It causes mild to severe nerve damage that, coupled with diabetes-related circulation problems, often leads to the loss of a leg or foot. Diabetes significantly increases the risk of heart disease. And it’s the seventh leading cause of death in the U.S., directly causing almost 70,000 deaths each year and contributing to thousands more. (4)

The good news is that type 2 diabetes is largely preventable. About 9 cases in 10 could be avoided by taking several simple steps: keeping weight under control, exercising more, eating a healthy diet, and not smoking.

What Is Type 2 Diabetes?

Our cells depend on a single simple sugar, glucose, for most of their energy needs. That’s why the body has intricate mechanisms in place to make sure glucose levels in the bloodstream don’t go too low or soar too high.

When you eat, most digestible carbohydrates are converted into glucose and rapidly absorbed into the bloodstream. Any rise in blood sugar signals the pancreas to make and release insulin. This hormone instructs cells to sponge up glucose. Without it, glucose floats around the bloodstream, unable to slip inside the cells that need it.

Diabetes occurs when the body can’t make enough insulin or can’t properly use the insulin it makes.

One form of diabetes occurs when the immune system attacks and permanently disables the insulin-making cells in the pancreas. This is type 1 diabetes, once called juvenile-onset, or insulin-dependent, diabetes. Roughly 5 to 10 percent of diagnosed diabetes cases are type 1 diabetes. (5)

The other form of diabetes tends to creep up on people, taking years to develop into full-blown diabetes. It begins when muscle and other cells stop responding to insulin’s open-up-for-glucose signal. The body responds by making more and more insulin, essentially trying to ram blood sugar into cells. Eventually, the insulin-making cells get exhausted and begin to fail. This is type 2 diabetes.

Type 2 diabetes used to be called adult-onset diabetes, since it was almost unheard of in children. But with the rising rates of childhood obesity, it has become more common in youth, especially among certain ethnic groups.

In the U.S., the SEARCH for Diabetes in Youth Study found that type 2 diabetes accounted for only 6 percent of new diabetes cases in non-Hispanic white children ages 10 to 19, but anywhere from 22 to 76 percent of new cases in other ethnic groups (6).The highest rates were found in Asia-Pacific Islander and Native American youth.

In addition to the millions of adults with diabetes, another 57 million adults have “pre-diabetes.” (7) This early warning sign is characterized by high blood sugar levels on a glucose tolerance test or a fasting glucose test. Whether pre-diabetes expands into full-blown type 2 diabetes is largely up to the individual. Making changes in weight, exercise, and diet can not only prevent pre-diabetes from becoming diabetes, but can also return blood glucose levels to the normal range.

Type 2 Diabetes Can Be Prevented

Although the genes you inherit may influence the development of type 2 diabetes, they take a back seat to behavioral and lifestyle factors. Data from the Nurses’ Health Study suggest that 90 percent of type 2 diabetes in women can be attributed to five such factors: excess weight, lack of exercise, a less-than-healthy diet, smoking, and abstaining from alcohol. (8)

Among 85,000 married female nurses, 3,300 developed type 2 diabetes over a 16-year period. Women in the low-risk group were 90 percent less likely to have developed diabetes than the rest of the women. Low-risk meant a healthy weight (body mass index less than 25), a healthy diet, 30 minutes or more of exercise daily, no smoking, and having about three alcoholic drinks per week.

Similar factors are at work in men. Data from the Health Professionals Follow-up Study indicate that a “Western” diet, combined with lack of physical activity and excess weight, dramatically increases the risk of type 2 diabetes in men. (9)

Information from several clinical trials strongly supports the idea that type 2 diabetes is preventable. The Diabetes Prevention Program examined the effect of weight loss and increased exercise on the development of type 2 diabetes among men and women with high blood sugar readings that hadn’t yet crossed the line to diabetes. In the group assigned to weight loss and exercise, there were 58 percent fewer cases of diabetes after almost three years than in the group assigned to usual care. (10) Even after the program to promote lifestyle changes ended, the benefits persisted: The risk of diabetes was reduced, albeit to a lesser degree, over 10 years. (11) Similar results were seen in a Finnish study of weight loss, exercise, and dietary change, and in a Chinese study of exercise and dietary change. (12-15)

Simple Steps to Lower Your Risk

Making a few lifestyle changes can dramatically lower the chances of developing type 2 diabetes. The same changes can also lower the chances of developing heart disease and some cancers.

Control Your Weight

Excess weight is the single most important cause of type 2 diabetes. Being overweight increases the chances of developing type 2 diabetes seven fold. Being obese makes you 20 to 40 times more likely to develop diabetes than someone with a healthy weight. (8)

Losing weight can help if your weight is above the healthy-weight range. Losing 7 to 10 percent of your current weight can cut your chances of developing type 2 diabetes in half.

Get Moving—and Turn Off the Television

Inactivity promotes type 2 diabetes. (16) Working your muscles more often and making them work harder improves their ability to use insulin and absorb glucose. This puts less stress on your insulin-making cells.

Long bouts of hot, sweaty exercise aren’t necessary to reap this benefit. Findings from the Nurses’ Health Study and Health Professionals Follow-up Study suggest that walking briskly for a half hour every day reduces the risk of developing type 2 diabetes by 30 percent. (18, 19) More recently, The Black Women’s Health Study reported similar diabetes-prevention benefits for brisk walking of more than 5 hours per week. (20) This amount of exercise has a variety of other benefits as well. And even greater cardiovascular and other advantages can be attained by more, and more intense, exercise.

Television-watching appears to be an especially-detrimental form of inactivity: Every two hours you spend watching TV instead of pursuing something more active increases the chances of developing diabetes by 20 percent; it also increases the risk of heart disease (15 percent) and early death (13 percent). (17) The more television people watch, the more likely they are to be overweight or obese, and this seems to explain part of the TV viewing-diabetes link. The unhealthy diet patterns associated with TV watching may also explain some of this relationship.

Tune Up Your Diet

Four dietary changes can have a big impact on the risk of type 2 diabetes.

There is convincing evidence that diets rich in whole grains protect against diabetes, whereas diets rich in refined carbohydrates lead to increased risk. In the Nurses’ Health Studies I and II, for example, researchers looked at the whole grain consumption of more than 160,000 women whose health and dietary habits were followed for up to 18 years. Women who averaged two to three servings of whole grains a day were 30 percent less likely to have developed type 2 diabetes than those who rarely ate whole grains. (21) When the researchers combined these results with those of several other large studies, they found that eating an extra 2 servings of whole grains a day decreased the risk of type 2 diabetes by 21 percent.

Whole grains don’t contain a magical nutrient that fights diabetes and improves health. It’s the entire package—elements intact and working together—that’s important. The bran and fiber in whole grains make it more difficult for digestive enzymes to break down the starches into glucose. This leads to lower, slower increases in blood sugar and insulin, and a lower glycemic index. As a result, they stress the body’s insulin-making machinery less, and so may help prevent type 2 diabetes. (22) Whole grains are also rich in essential vitamins, minerals, and phytochemicals that may help reduce the risk of diabetes.

In contrast, white bread, white rice, mashed potatoes, donuts, bagels, and many breakfast cereals have what’s called a high glycemic index and glycemic load. That means they cause sustained spikes in blood sugar and insulin levels, which in turn may lead to increased diabetes risk. (22) In China, for example, where white rice is a staple, the Shanghai Women’s Health Study found that women whose diets had the highest glycemic index had a 21 percent higher risk of developing type 2 diabetes, compared to women whose diets had the lowest glycemic index. (23) Similar findings were reported in the Black Women’s Health Study. (24)

More recent findings from the Nurses Health Studies I and II and the Health Professionals Follow-Up Study suggest that swapping whole grains for white rice could help lower diabetes risk: Researchers found that women and men who ate the most white rice—five or more servings a week—had a 17 percent higher risk of diabetes than those who ate white rice less than one time a month. People who ate the most brown rice—two or more servings a week—had an 11 percent lower risk of diabetes than those who rarely ate brown rice. Researchers estimate that swapping whole grains in place of even some white rice could lower diabetes risk by 36 percent. (25)

2. Skip the sugary drinks, and choose water, coffee, or tea instead.

Like refined grains, sugary beverages have a high glycemic load, and drinking more of this sugary stuff is associated with increased risk of diabetes. In the Nurses’ Health Study II, women who drank one or more sugar-sweetened beverages per day had an 83 percent higher risk of type 2 diabetes, compared to women who drank less than one sugar-sweetened beverage per month. (26)

Combining the Nurses’ Health Study results with those from seven other studies found a similar link between sugary beverage consumption and type 2 diabetes: For every additional 12-ounce serving of sugary beverage that people drank each day, their risk of type 2 diabetes rose 25 percent. (27) Studies also suggest that fruit drinks— Kool Aid, fortified fruit drinks, or juices—are not the healthy choice that food advertisements often portray them to be: Women in the Black Women’s Health study who drank two or more servings of fruit drinks a day had a 31 percent higher risk of type 2 diabetes, compared to women who drank less than one serving a month. (28)

How do sugary drinks lead to this increased risk? Weight gain may explain the link: In both the Nurses’ Health Study II and the Black Women’s Health Study, women who increased their consumption of sugary drinks gained more weight than women who cut back on sugary drinks. (26, 28) Several studies show that children and adults who drink soda or other sugar-sweetened beverages are more likely to gain weight than those who don’t, (28, 30) and that switching from these to water or unsweetened beverages can reduce weight. (31) Even so, however, weight gain caused by sugary drinks may not completely explain the increased diabetes risk. There is mounting evidence that sugary drinks contribute to chronic inflammation, high triglycerides, decreased “good” (HDL) cholesterol, and increased insulin resistance, all of which are risk factors for diabetes. (32)

What to drink in place of the sugary stuff? Water is an excellent choice. Coffee and tea are also good calorie-free substitutes for sugared beverages (as long as you don’t load them up with sugar and cream). And there’s convincing evidence that coffee may help protect against diabetes; (33, 34) emerging research suggests that tea may hold diabetes-prevention benefits as well, but more research is needed.

There’s been some controversy over whether artificially sweetened beverages are beneficial for weight control and, by extension, diabetes prevention. (35) Some studies have found that people who regularly drink diet beverages have a higher risk of diabetes than people who rarely drink such beverages, (36, 37) but there could be another explanation for those findings: People often start drinking diet beverages because they have a weight problem or have a family history of diabetes; studies that don’t adequately account for these other factors may make it wrongly appear as though the diet soda led to the increased diabetes risk. A recent long-term analysis on data from 40,000 men in the Health Professionals Follow-Up Study finds that drinking one 12-ounce serving of diet soda a day does not appear to increase diabetes risk. (38) So in moderation, diet beverages can be a good sugary-drink alternative.

3. Choose good fats instead of bad fats.

The types of fats in your diet can also affect the development of diabetes. Good fats, such as the polyunsaturated fats found in liquid vegetable oils, nuts, and seeds can help ward off type 2 diabetes. (39) Trans fats do just the opposite. (8, 40) These bad fats are found in many margarines, packaged baked goods, fried foods in most fast-food restaurants, and any product that lists “partially hydrogenated vegetable oil” on the label. Eating polyunsaturated fats from fish—also known as “long chain omega 3” or “marine omega 3” fats—does not protect against diabetes, even though there is much evidence that these marine omega 3 fats help prevent heart disease. (41) If you already have diabetes, eating fish can help protect you against a heart attack or dying from heart disease. (42)

The evidence is growing stronger that eating red meat (beef, pork, lamb) and processed red meat (bacon, hot dogs, deli meats) increases the risk of diabetes, even among people who consume only small amounts. The latest support comes from a “meta analysis,” or statistical summary, that combined findings from the long-running Nurses’ Health Study I and II and the Health Professionals Follow-Up Study with those of six other long-term studies. The researchers looked at data from roughly 440,000 people, about 28,000 of whom developed diabetes during the course of the study. (43) They found that eating just one daily 3-ounce serving of red meat—say, a steak that’s about the size of a deck of cards—increased the risk of type 2 diabetes by 20 percent. Eating even smaller amounts of processed red meat each day—just two slices of bacon, one hot dog, or the like—increased diabetes risk by 51 percent.

The good news from this study: Swapping out red meat or processed red meat for a healthier protein source, such as nuts, low-fat dairy, poultry, or fish, or for whole grains lowered diabetes risk by up to 35 percent. Not surprisingly, the greatest reductions in risk came from ditching processed red meat.

Why do red meat and processed red meat appear to boost diabetes risk? It may be that the high iron content of red meat diminishes insulin’s effectiveness or damages the cells that produce insulin; the high levels of sodium and nitrites (preservatives) in processed red meats may also be to blame. Red and processed meats are a hallmark of the unhealthful “Western” dietary pattern, which seems to trigger diabetes in people who are already at genetic risk. (44)

If You Smoke, Try to Quit

Add type 2 diabetes to the long list of health problems linked with smoking. Smokers are roughly 50 percent more likely to develop diabetes than nonsmokers, and heavy smokers have an even higher risk. (45)

Alcohol Now and Then May Help

A growing body of evidence links moderate alcohol consumption with reduced risk of heart disease. The same may be true for type 2 diabetes. Moderate amounts of alcohol—up to a drink a day for women, up to two drinks a day for men—increases the efficiency of insulin at getting glucose inside cells. And some studies indicate that moderate alcohol consumption decreases the risk of type 2 diabetes. (8, 46-51) If you already drink alcohol, the key is to keep your consumption in the moderate range, as higher amounts of alcohol could increase diabetes risk. (52) If you don’t drink alcohol, there’s no need to start—you can get the same benefits by losing weight, exercising more, and changing your eating patterns.

The Bottom Line: Preventing Type 2 Diabetes

They key to preventing type 2 diabetes can be boiled down to five words: Stay lean and stay active.

References

1. American Diabetes A. Economic Costs of Diabetes in the U.S. in 2007. Diabetes Care. 2008; 31:596-615

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